1. Field of the Invention
The present invention relates to a microresonator including a beam-type resonator element that is electrostatically driven, a band-pass filter including this microresonator, a semiconductor device including this microresonator, and a communication apparatus that uses a band-pass filter based on this microresonator.
2. Description of the Related Art
With progress in wireless communication technology in recent years, there has been demand for size reduction and weight reduction in a communication apparatus that uses wireless communication technology. Micro-electro-mechanical-system (MEMS) technology, which employs micro-processing technology used for a semiconductor to manufacture a micro mechanical structure, has been used for an RF signal processing portion where size reduction has been hitherto considered to be difficult. As an example thereof, there is a mechanical filter using mechanical resonance, which is expected to be applied to a communication field, because size is small and integration is possible.
Japanese Published Patent Application No. 2004-328076 discloses a beam-type microresonator element that is electrostatically driven, as a mechanical resonator element constituting a filter. As shown in FIGS. 1A and 1B, a microresonator element 1 is configured such that an input electrode 3 and an output electrode 4 that are lower electrodes are formed on a substrate 2 having at least an insulating surface. Further, an electrode to be an oscillating portion, that is, a beam 6 is formed opposing those input electrode 3 and output electrode 4 across a space 5. The input electrode 3 and the output electrode 4 are formed to intersect the lengthwise direction of the beam 6. The beam 6 straddles the input and output electrodes 3, 4 in the manner of a bridge and is integrally supported at both ends by support portions (anchor portions) 8 [8A, 8B] to be connected to wiring layers 7 disposed outside the input and output electrodes 3, 4. A necessary DC bias voltage VDC is applied to the beam 6 through the wiring layer 7.
In this microresonator element 1, based on a signal input from the input electrode 3, the beam 6 oscillates at a specific resonance frequency, because the beam 6 receives external force caused by electrostatic force generated between the beam 6 to which a DC bias voltage VDC is applied and the input electrode 3. This oscillation is transmitted as a signal to the output electrode 4 through the micro space 5.